The present invention relates to methods for treating Alzheimer""s Disease (AD). More specifically, the present invention relates to methods of treating AD by inhibiting Axcex2-induced microglial activation.
Alzheimer""s disease (AD) is a neurodegenerative disease characterized by the presence of extracellular amyloid deposits (composed mainly of Axcex2) and intraneuronal tangles (consisting of the cytoskeletal protein tau) in specific brain regions. Increased phosphorylation of tau is thought to result in neurofibrillary tangles in AD brains and with AD-like pathology in transgenic models of the disease [Genis et al., 1999; Schneider et al., 1999; Sturchler-Pierrat et al., 1997; James et al., 1996; Higgins et al., 1995].
The symptoms of AD include gradual loss of short-term memory, declined ability to perform routine tasks such as eating, confusion, disorientation, the inability of the patient to care for him or herself, and eventually death. The American Health Assistance Foundation has reported that, presently, more than four million Americans are believed to have AD. Furthermore, each year 250,000 new cases of AD are diagnosed and 100,000 Americans die because of AD. Moreover, one out of every ten Americans 65 years and older have AD and almost half of those 85 years and older have the disease.
The inflammatory component of AD is becoming increasingly substantiated as a major contributor to the AD pathogenic process. However, treatment strategies aimed at lessening the negative effects of inflammation in AD are only available to a very limited extent. Furthermore, rather than targeting AD-associated neuro-inflammation, these drugs tend to be general inhibitors of inflammation (such as non-steroidal anti-inflammatory agents like aspirin) which only provide partial therapeutic benefit (Rich, J. B., Rasmusson, D. X., Folstein, M. F., Carson, K. A., Kawas, C. and Brandt, J. Nonsteroidal anti-inflammatory drugs in Alzheimer""s disease. Neurology 45, 51-55 (1995).
Amyloid xcex2 peptides (Axcex2)have long been thought to be central to the neuropathology of Alzheimer""s disease (AD) [Glenner and Wong, 1984]. Axcex2 peptides activate microglia, resident immune cells in the brain, resulting in markedly increased levels of the pro-inflammatory acute phase cytokine tumor necrosis factor-xcex1 (TNF-xcex1 release) [Meda et. al., 1999; Klegeris et. al., 1997]. At these high levels secreted by microglia, TNF-xcex1 has been shown to be neurotoxic (Tan et al., Journal of Neuroimmunology, 1999). For example, high doses ( greater than 11 xcexcM) of Axcex21-42 are able to produce increased TNF-xcex1 production in microglial cells [Meda et. al., 1999]. However, such doses of Axcex21-42 rapidly produce large amounts of Axcex2 fibrils and loss of Axcex2 solubility in vitro [Castillo et al., 1997; Genis et al., 1999; Schneider et al., 1999; Sturchler-Pierrat et al., 1997; James et al., 1996; Higgins et al., 1995].
Previously, it has been suggested that Axcex2 activation of microglial cells may be involved in the inflammatory component of AD. The data indicate that Axcex2 can stimulate pro-inflammatory responses in microglia, including elevated cytokine release, nitric oxide synthase expression, nitric oxide production, and neurotoxicity [Meda, et al., 1995; Combs, et al., 1999; Kalaria, 1999]. However, the mechanisms of Axcex2-induced microglial activation remain speculative, and often require a co-stimulatory factor such as the pro-inflammatory cytokine interferon-xcex3.
Since inflammatory processes are major contributors to AD pathophysiology and CD40, as an important cellular signaling and activation antigen, plays a key role in inflammatory processes [Schonbeck et al., 1997; Sempowski et. al., 1997; Karmann et. al., 1995], CD40 may play a key role in AD. Furthermore, as a neuroimmune response has previously been thought to be implicated in AD pathogenesis [Cacabelos R, Med Clin (Barc) Mar 26, 1994; 102(11): 420-2; McGeer P L, Rogers J, McGeer E G, Alzheimer Dis Assoc Disord 1994 Fall; 8(3): 149-58; Dickson, D W and Rogers, J, Neurobiol Aging 1992 November-December; 13(6): 793-8], and CD40 is functionally expressed on microglia [Tan et al., 1999, Journal of Neuroimmunology; Tan et al., 1999, Journal of Immunology], the possibility arises that CD40 may additionally mediate a pathogenic neuroimmune response in AD. However, it has not previously been established what, if any, role CD40 plays in the AD pathogenic process, nor how to utilize this knowledge in potential treatments of AD.
It would, therefore, be useful to determine the role that CD40 plays in AD. It would also be useful to develop methods for treating AD by modulating the CD40 pathway.
According to the present invention, there is provided an assay method for determining the effect of an agent on Alzheimer""s Disease pathology by treating microglial cells with Axcex2 peptides, adding CD40 ligand to the microglial cells, adding a therapeutic agent to the microglial cells, and measuring Alzheimer""s Disease pathology. Also provided is a method of determining therapeutic effectiveness of an agent for Alzheimer""s Disease by measuring the inhibition of CD40-CD40L binding and/or its functional outcomes in the presence of the agent. A method of testing the efficacy of a therapeutic agent by producing Tg APPsw and Tg APPsw/CD40L deficient mice and administering to these mice the therapeutic agent to be tested and determining the efficacy of the drug in suppressing Alzheimer""s disease-like pathology is also provided. An assay for determining the effect of an agent on Alzheimer""s Disease pathology by treating microglial cells with Axcex2 peptides, co-treating these cells with CD40 ligand, adding a therapeutic agent to the microglial cells and utilizing a measuring device for quantifying Alzheimer""s Disease pathology is also provided.